A. Field of the Invention
The present invention relates generally to two-way communication and control network systems, and, more particularly, to communication and control networks of the type disclosed in the above-identified related applications wherein a communication and control network provides communication between a variety of control devices such as circuit breakers, motor starters, protective relays, remote load controllers, lighting systems, and the like, to communicate with and be controlled by a central or master controller over a common network line. Specifically, the present invention is directed to certain aspects of a communication and control system which employs a multipurpose software based microcontroller which can be operated in a master mode in which the microcontroller interfaces an external host computer, or terminal, to the communication and control network through a hardware-based digital IC of the type disclosed in said above-identified related applications, said microcontroller also being operable in an expanded slave mode in which a controlled product connected to the microcontroller is interfaced to the common network line through the same or similar hardware-based digital IC.
B. Description of the Prior Art
In the communication and control system disclosed in the above-identified related applications control and monitoring is carried out over a network consisting of either the existing power lines or a dedicated twisted pair of lines. The hardware-based digital integrated circuit described in detail in the Verbanets application Ser. No. 625,747 identified above forms the basic building block for such a communication and control network. This digital IC is a twenty-eight pin semi-custom integrated circuit implemented by complementary metal oxide semiconductor (CMOS) technique which provides a simple, low cost interface to the communication and control network. This digital IC, which may also be referred to as an industrial communication (INCOM) integrated circuit, or chip, provides the network interface functions of address recognition, detection and storage of an on-off keyed carrier multi-bit message received from the network, carrier generation and transmission of an on-off keyed carrier message to the network in accordance with the information stored therein, generation and checking of a five bit BCH error checking code, and framing of the received and transmitted messages.
The digital IC, or INCOM chip, may be configured for one of three operating codes: stand alone slave, expanded-mode slave and expanded-mode master. Arbitration of the network is accomplished in a master-slave fashion. The stand alone slave mode is used by simple devices and provides control of a single output line and the return of two status bits from the slave device. The expanded-mode slave is used to interface microprocessor based equipment to the network and will support far more complex communications between the master and the expanded-mode slave. When the INCOM chip is operated in an expanded master mode, the INCOM device may be used as a direct interface to the master or central controller of the network. However, in many instances it is desirable that the network master use a conventional RS232C serial link or equivalent, to communicate with the stand alone slaves and enabled mode slaves on the network. The ASCII protocol normally used with such a serial link is, however, not compatible with the 33 bit message format employed by the INCOM network. Accordingly, this severely limits the types of computers or terminals which can be used as a master or central controller for the INCOM network.
When the INCOM chip is operated in the expanded slave mode it may be used as a direct interface to a microprocessor controlled product. However, in many instances the microprocessor associated with the controlled product may be quite busy and hence cannot be directly coupled to the network through the INCOM chip. This is particularly true of products such as motor starters and controllers in which many different variables, such as rotor winding temperature, bearing temperature, ground fault, overcurrent, locked rotor current, and underload and overload voltages may be monitored and/or controlled. Furthermore, even if the microprocessor associated with a controlled product is relatively inactive, it is in many instances desirable to provide an intermediate buffer interface between the INCOM chip and the controlled product so that a major design change or reprogramming of the microprocessor associated with the product is not required in order to utilize the INCOM network.